Voltage regulator



7, 1951 J. A. POTTER 2,563,486

" VOLTAGE REGULATOR Filed Dec. 24, 1949 FIG. 2

1.040 CURRE/VT lazauu r50 0. c. SUPPL r lNl/ENTOR J. A. POTTER ATTORNEYPatented Aug. 7, 1951 UNITED STATES PATENT OFFICE 2,563,486 VOLTAGEREGULATOR James A. Potter, Rutherford, N. 1., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication December 24, 1949, Serial No. 134,916

1 20 Claims.

This invention relates to current and voltage regulation andparticularly to regulated rectifier apparatus for'supplying directcurrent to a load circuit- More' specifically. the invention hereinrelates to improvements in the regulated rectifying apparatus disclosedin my copending application, Serial No. 764,490, filed July 29, 1947.

. It is an object of this invention toprovide improved regulatingapparatus for controlling the supply of current to a load.

It is a further object of the invention to provide apparatus forregulating the current supplied to a load to minimize load voltagechanges, and, when the current required for constant volt-' age isexcessive, for regulating the current supplied to the load to minimizethe load current changes.

Another object is to provide sharp and stable cut-over from voltage tocurrent regulation, or vice versa, in such apparatus at a predeterminedload current.

It is also an object to prevent excessive overloads in the event of afailure within the regulating apparatus.

It is a further object of the invention to stabilize parallel operationof regulated rectifiers.

In an illustrative embodiment of the invention herein shown anddescribed, the circuit which supplies alternating current to a bridgetype rectifier contains a saturable reactor. The output of the rectifieris regulated by controlling the current supplied to the direct currentwinding of the reactor. From no load to a current in the vicinity offull load the rectifier is so regulated as to maintain the load voltageconstant. If the current required for constant voltage is excessive,control of the rectifier is transferred so that the load current is heldconstant despite further decreases in the load voltage. If there shouldbe a failure within the regulator apparatus, further means are alsoprovided to prevent excessive overloads.

Electronic switching means comprising a pair of triodes connected inparallel and operated jointly as a cathode follower efiect the transferfrom constant voltage regulation to constant current regulation. Thegrid voltage of one triode is caused to decrease in proportion todecreases in load voltage while the grid voltage of the other triode iscaused to increase in proportion to increases in the load current. Onlythe space current path with the more positive grid will conduct so thatby making the grid which is responsive to load voltage variations themore positive at no load, the net space current will be a function ofthe load voltage until the grid responsive to load current variationsshall have become the more positive. The net space current of thesetriodes controls a regulator tube connected in series with theaforementioned circuit supplying direct current to the saturable reactorand hence controls the supply of alternating current to the rectifier.The gain of the triodes permits sharp cut-over from voltage to currentregulations, or, vice versa, and, since both tubes will be conducting inthe region that the control is transferred, the switching action will bestable.

If several regulated rectifiers are to be operated in parallel to supplya load, it is desirable from the standpoint of overall efliciency thatthey share the load equally, assuming them to be of equal power rating.At the time of installation they may be manually adjusted so as toproperly share the load. Due to their extremely fiat characteristics,however, a change of but a fraction of a volt, for example, due to agingof some of the component parts, may result in a change in output currentof well over fifty amperes. To prevent one regulator from grabbing allof the load if its operating point should shift, the voltage controlamplifiers of identical rectifiers are con- .nected in parallel by meansof relatively high impedance couplings. Variations within any oneregulator are thus reflected to each of the other regulators by anamount determined by the size of the coupling resistors which causes theregulator outputs to track one another.

The invention will be more clearly understood from the followingdetailed description of an illustrative embodiment when read inconnection with the attached drawing in which:

Fig. 1 is a schematic view of a regulated rectifier embodying theinvention; and

Fig. 2 shows characteristic curves of such a rectifier.

Referring now to Fig. 1, a single phase bridge rectifier I ll comprisingselenium rectifying elements H is connected to supply current through asmoothing choke [2 to a battery I3 across which a load H, which mayvary, is connected. The choke l2 and the capacitance of the battery I3form a filter across the rectifier output.

Power is supplied to the rectifier Ill from an alternating currentsource l5 through an input transformer I6. The primary winding of thetransformer is is in series with a buck-boost auto-transformer l1 andthe paralleled windings current in the saturating winding IS in thefollowing manner.

Series current through the be winding of the auto-transformer H from thesource !5 induces a voltage in the ac winding thereof which reduces thevoltage across the primary winding 16 and hence bucks" the supply ofpower to the rectifier. This action, however, is opposed by current fromthe source 15 which flows through the ab winding of the auto-transformerll. This latter current induces a voltage in the be winding, which addsto the voltage across the primary winding of the transformer I6 andhence boosts" the supply of power to the rectifier.

If no current flows through the auto-transformer winding ab from thesource l5, the voltage appearing across the primary of the transformer16 will be equal to the voltage of the source l5 less a voltage drop dueto the inductive reactance of the winding be. This condition will be metat zero load when there is no current flowing in the saturating windingI9 of the reactor I8 and the voltage drop across the winding 'be is highenough to leave only a small percentage of the source l5 voltage acrossthe transformer l6 primary. To further reduce the selenium rectifierinput voltage to zero at no load, the transformer I6 is designed torequire a relatively high magnetizing current. Efi'ectively, thisresults in approximately zero voltage across the secondary of thetransformer l6.

As the load current increases, current through the saturating winding I9is also caused to increase, thereby reducing the inductance and henceinductive reactance of the saturable reactor [8 to allow series currentto fiow through the ab winding of the auto-transformer I! from thesource I5. This latter current induces a current in the winding be whichis opposite in direction to that flowing from the source 15 through thewinding be and the transformer l6 primary in series and hence opposesthe voltage drop due to the series current. When the induced current inthe winding be equals the series current therethrough, the voltageacross the transformer l6 primary will equal the source l5 voltage.Further increases in the load current will result in a higher inducedcurrent in the winding be so that the voltage across the transformer l6primary will be increased above that of the source l5.

The condenser 20 and inductance 2| form a filter which is tuned to thethird harmonic of the source l5 frequency and which acts to eliminateany such harmonics which may appear in the ac winding of theauto-transformer IT. The resistor 22 limits current which may be inducedin the saturating winding l9 from voltage surges across the parallelwindings of the reactor l8.

This buck-boost arrangement comprising an auto-transformer and asaturable reactor permits an important saving in iron since the inputvoltage may be varied both above and below the normal value of thesource l5 by varying the current in the saturating winding of thereactor. If only a saturable reactor is used to control the inputvoltage, being connected either in series or in parallel with the powersource, the input voltage can be varied only in one direction from thenormal value, thus requiring a reactor of approximately twice the iron,other factors being equal.

The regulator circuits whereby the power supplied to the rectifier is'controlled will now be described briefly as background for the detaileddescription to follow.

Current for the saturating winding 19 of the saturable reactor issupplied by the rectifying tube 25 and is controlled by the seriesregulating tube 23. The direct current supply is filtered by thecondenser 24. The regulating circuit comprises an amplifier, called avoltage amplifier herein, comprising a space current triode 3|, 2.second amplifier, called a current amplifier herein, comprising twospace current triodes 32 and 33, a final or output amplifier comprisinga space current triode 34, and an electronic switch comprising two spacecurrent triodes 35 and 36 for alternatively connecting the output of thevoltage or current amplifiers to the input of the final amplifier stage.The series regulating device 23 is under the control of the finalamplifier 34 and the outputs of the voltage and current amplifiers areadjusted so that at load currents below a certain value the rectifierwill be operated as a constant voltage device. At higher load currents,however, the electronic switch will transfer control to the currentcontrol amplifiers so that constant current operation will be in effect.If there should be a failure within the regulator circuit, abnormal loadcurrents will cause the relay 3'] to operate. This operation of relay 3!acts to reduce the input-to the rectifier l6 and hence limits the loadcurrent to a safe value.

The circuits for regulating the supply of power to the rectifier willnow be described in detail. There are provided a regulateddirect-current supply source 38, as is more fully disclosed in myaforementioned copending application, and an unregulated direct-currentsource 39 comprising the rectifier 40 and filter condenser 4|. Thepositive terminal of the regulated supply is connected to the negativeterminal of the unregulated supply by the lead 42. These sources serveas anode and filament supplies for the various space discharge devicesand as sources of potential as needed in the regulating circuits.Circuits for supplying the filaments of the various tubes have not beenindicated in the drawing but heating current could be supplied from thesource 33 in a readily obvious manner.

The space current path for the output amplifier tube 34 may be tracedfrom its cathode through the resistance '43 to the negative terminal ofthe battery l3, from the positive terminal of the battery through theresistor 44 and the lead 45 to the negative terminal of the regulatedsupply 38, from the positive terminal thereof through lead 42 to thenegative terminal of the unregulated supply 39, and from the positiveterminal thereof through resistor 46 to the anode of tube 34. A

condenser 41 is connected between the control grid and cathode of thetube 34 to eliminate ripple, stray R. F. and parasitics from the grid ofthe tube. It will be noted that the control grid-cathode circuit of thetube 23 includes, in series, the resistor 46, the condenser 4| and theresistors 48 and 49 so that the effective resistance of the spacecurrent path of the series regulating tube 23 is controlled in responseto variations in the space current of tube 34 which varies the voltagedrop across resistor 46. Resistor 49 and condenser 50 cooperate as afilter to remove high frequency components from the control grid of tube23; The fixed bias for tube 23 is equal to the difierence in voltageacross condenser 4| and resistors 48 and 49 and is adjusted so that at.no load no current will flow through the saturating winding 19 forreasons hereinbefore described. Fixed bias for the tube 34 is suppliedby a voltage divider comprising resistors 5| and 52 which are connectedacross the output of the regulated supply 38.

Resistor 53 is connected across the terminals of the battery l3 and isincluded in the space current path of tube 3| which may be traced fromthe positive terminal of the battery 53, through resistor 44 and lead 45to the negative terminal of the regulated supply 38, from the positiveterminal of the regulated supply to the negative terminal of theunregulated supply 39, from the positive terminal of the unregulatedsupply through resistor 54 to the anode of tube 3|, and from the cathodethereof through resistors 55 and '53 to the negative terminal of thebattery l3. A filter condenser 56 interconnetcs the control grid andcathode of the tube 3|. The anode of tube 3| is directly connected tothe control grid of tube 35. A control grid-cathode circuit for the tube35 may be traced from the cathode through the resistor 43 to thenegative terminal of the battery I3, from the positive terminal of thebattery through resistor 44 and the lead 45 to the negative terminal ofthe regulated supply 38, from the positive terminal thereof to the negative terminal of the unregulated supply 39, and from the positiveterminal thereof through the resistor 54 returning to the grid. Althoughthe battery I3 is also included in the space current path of tube 35,the unamplified voltage variations of the battery have substantially nodirect eflect on the grid-cathode voltage of the tube. Rather, the gridvoltage of tube 35 is varied in accordance with the variations ofbattery l3 voltage which are amplified by the tube 3| and which resultin a change in voltage drop across the resistor 54. A filter condenser5'! interconnects the control grid and cathode of the tube 35.

The aforementioned resistors 53 and 55 com-.

prise, in series, one arm of a bridge circuit 5|. which has as its otherarms a symmetrical varistor 52 shunted by a potentiometer 63 having avariable tap 64, a directly heated thermistor 65 shunted by a resistor53 and in series with another resistor 61, and a resistor 68. Thevaristor provides a stable reference voltage across its terminals since,in its operating region, it is essentially a constant voltage device.The thermistor 85 and resistors 86 and 31 are provided to compensate forthe resistance-temperature characteristic of the-varistor 32 since theresistance of the varistor and hence the voltage drop across it tends todecrease with increasing ambient temperature.

Therefore, if the ambient temperature should rise, for example, theresistance of the thermistor 83 decreases to cause the current throughthe varistor 62 to rise and thereby minimize the eflfect of ambienttemperature chariges on the voltage drop across the varistor. Anyvoltage variations which may occur will appear mainly across theresistor 81. r

The positive terminal of the regulated supply 38 is connected to one ofthe bridge terminals and the opposite terminal of the bridge isconnected to the negative terminal of the battery l3 so that the sum ofthe voltages of the battery l3 and the supply 38 appears across thesetwo terminals. The potentiometer 83 with its variable -tap forms avoltage divider across the varistor 62 and is connected by way of thetap 64 to the control grid of the tube 3|. The remaining terminal of thebridge is connected to the cathode of the tube 3| so that the voltagederived by the bridge circuit and impressed on the grid-cathode circuitof the voltage amplifier 3| is equal to the sum of the voltages acrossthe resistors 55 and 53 minus as much of the voltage across the varistor62 that appears between the adjustable tap 64 and the negative terminaloi. the bridge 6|. Since the varistor voltage remains substantiallyconstant with changes in current, any change in the battery I3 voltagewill be reflected as a change in the grid-cathode voltage of the tube3|. Therefore, as the voltage of the battery l3 increases, for example,the voltage across the output terminals of the bridge also increases tomake the control grid of the tube 3| more negative with respect to itscathode. -This reduces the space current in the tube 3| and hence raisesthe potential of its anode, and, due to the direct connection of theanode of tube 3| and the control grid of the tube 35, this increase inanode potential results in an increase in the control grid-cathodepotential of the tube 35. Thus, the grid-cathode voltage of tube 35increases in proportion to increases in the battery l3 voltage. As willbe described later, this increase in grid voltage acts to decrease thepower input to the rectifier- III and hence hold the load voltageconstant.

The space current circuit for the current amplifier tube 33 may betraced from the negative terminal of the regulated supply 38 through thepositive terminal thereof to the negative terminal of the unregulatedsupply 39, from thepositive terminal of the unregulated supply throughthe resistor 89 to the anode of tube 33, from the cathode of tube 33 tothe anode of tube 32, and

I the movable tap 14 of the potentiometer 13 and the negative terminalof the regulated supply which is applied to the control grid of tube 33.The unregulated supply 39 and the reference voltage potentiometer 13 areconnected together through resistor 15. A change in the unregulatedsupply voltage will therefore cause a change in the grid voltage of thetube 33 in the same direction. The combined effect of these two actionsis to leave the anode voltage of the tube 33 unchanged by variations inthe unregulated supply.

The space current path for the tube 32 may be traced from the negativeterminal of the regulated supply 38 to the positive terminal thereof,from the positive terminal through the resistor I5 to the anode of tube32 and from the cathode thereof through the resistor I0, returning tothe negative terminal of the supply 38. The resistor 18 providesnegative feedback for the tube 32 and thus reduces the gain of the firststage of the current amplifier. A filter condenser 11 interconnects thegrid and cathode 'of the tube 32. The control grid-cathode path for thetube 32 may be traced from the grid through a resistor 18 whichcooperates with the filter condenser 11, through the resistor 44 and thelead 45 to the negative terminal of the regulated supply 38, andreturning through the cathode resistor 10 to the cathode of the tube.The voltage variations across the resistor 44 are proportional tovariations in the amplitude of the current supplied by the rectifier illto the battery |3 and load l4 and are thus impressed upon thegrid-cathode circuit of the tube 32. The control grid-cathode circuit ofthe tube 33 includes, in addition to a portion 01' the potentiometer 13and the resistor 12, the resistor 13; hence. load current variations do-This 2,ses,4se

tected as voltage variations by the resistor 42 are reflected in thespace current of the tube 33.

The control grid of tube 36 is directly connected to the anode of tube33 similarly to the connection of the grid of the tube 35 to the anodeof tube 3|. Likewise, the control grid-cathode circuit for tube 35 maybe traced from the cathode through the resistor 43 to the negativeterminal of battery l3, from the positive terminal through resistor 44and lead 45 to the negative terminal of the regulated supply 38 andunregulated supply 49 to the positive terminal of the latter, and fromthere through the resistor 69 to return to the grid. A filter condenser19 interconnects the grid and cathode of tube 36. And, as with tube 35,the unamplified variations of battery |3 voltage have substantially nodirect efiect on the grid voltage of tube 36 since the battery |3 isincluded in both the space current and grid-cathode paths of the tube.The space current of tube 36 will, therefore, be varied in accordancewith the variations in the space current of tube 33, with increase inthe latter causing a decrease in the grid-cathode voltage of tube 36 andvice versa. It may thus be seen that as the load current increases, forexample, the voltage drop across the resistor 44 will increase makingthe grid of tube 32 more negative with respect to its cathode. This willdecrease the space current in the tube 32 and increase the potential ofits anode. Consequently, the grid of tube 33 will become more negativewith respect to its cathode and cause a decrease in the space current oftube 33. This decrease in space current will decrease the voltage dropacross resistor 69 and hence increase the grid-cathode voltage of tube36. As will be described later, thi increase in grid voltage will act todecrease the power input to the rectifier I6 and hence prevent furtherincreases in load current.

It has now been described how an increase in battery l3 voltage drivesthe'grid of tube 35 more positive with respect to its cathode and how anincrease in the load current results in an increase of the grid-cathodevoltage of the tube 36. Opposite trends in load voltage and currentwill, of course, drive the respective grids more negative. It will nowbe described how these grid voltages operate to transfer control of therectifier from the voltage amplifier 3| to the current amplifier 3233 ifthe current required to maintain the load voltage constant becomesexcessive.

The tubes 35 and 36 are connected in parallel and the common portion oftheir space current paths may be traced from their common cathodeconnection through a common cathode resistor 43 to the negative terminalof the battery l3, from the positive terminal of battery I3 through theresistor 44 and lead 45 to the negative terminal of the regulated supply38, from the positive terminal of the regulated supply to the negativeterminal of the unregulated supply 39, and from the positive terminal ofthe unregulated supply to their common anode connection.

The common cathode resistor 43 is included in the grid-cathode circuitof the tube 34 which may be further traced through battery l3, resistor44 and lead 45 to the negative terminal of the regulated supply 38 andfrom there through resistor 52 to the grid of tube 34. Variations in thenet space current of the paralleled tubes 35 and 36 are amplified by thetube 34 which, as previously described, controls the resistance of thespace current path of the series regulator tube 23.

'of the saturable reactor.

An increase in the current through the resistor 43, for example, due toan increase in the grid potential of either tube 35 or 36 will increasethe voltage drop across resistor 43 and hence decrease the grid-cathodepotential of tube 34. This decrease in grid potential will decrease thespace current in tube 34 and hence decrease the voltage drop acrossresistor 44 and make the cathode of tube 23 more positive with respectto its grid. This increases the resistance of the space current path oftube 23 and decreases the current in the saturating winding l9 Asexplained hereinbefore, a decrease in saturating current will decreasethe boosting action of the autotransformer and efiect a decrease in thevoltage input to the rectifier l0. Decreases in the grid voltages ofeither tubes 35 or 36 will result in increased saturating current andhence increased power input to the rectifier Ill.

The tubes 35 and 36 are connected to operate jointly as acathode-follower, and form an electronic switch which acts toalternatively connect the voltage amplifier 3| or the current amplifier3233 to the final amplifier 34. The anodes of tubes 35 and 36 areconnected to the positive side of the unregulated supply 39 while thecommon cathode resistor 43 is connected to the negative terminal of thebattery l3. At no load the control grid of tube 35 is much more positivethan the control grid of tube 36 with respect to their common cathodeconnection. The resultant space current fiowing through cathode resistor43 raises the potentials of the cathodes of tubes 35 and 36 to a levelwhere the tube 36 is cut ofi. Thus, only the voltage amplifier 3| isconnected to the final amplifier 34 and space current variations in thecurrent control amplifier 32-33 will have no efiect on the rectifierinput. The rectifier Ill, therefore, is under constant voltageregulation.

As the load increases, the load voltage will tend to decrease whichdrives the control grid of tube 35 more negative and results in anincrease of the power input to the rectifier ID as previously described.At the same time the increased current flowing to the load through theresistor 44 drives the grid of tube 36 more positive. At a. load currentpredetermined by the settings of the potentiometers l3 and 63, thecombined efiects of the cathodes of tubes 35 and 36 becoming lesspositive due to decreased plate current and the grid of tube 36 becomingmore positive due to increased load current causes the tube 36 to beginto conduct. As the load current continues to increase, the grid voltageof tube 36 will also continue to increase and the increasing spacecurrent will again tend to drive the cathodes more positive. At the sametime, due to the decreasing load voltage, the grid voltage of tube 35continues to decrease so that these combined effects will cut off spacecurrent in the tube 35. The voltage amplifier 3| is thereforedisconnected from the final amplifier 34 and the current amplifier 32-33alone remains connected thereto, placing rectifier I0 under constantcurrent regulation. Further tendencies of the load current to increasewill result in decreasing the power input to the rectifier In aspreviously de scribed so that the load current will be maintainedconstant at a value substantially equal to the load current at which thetube 35 becomes cut ofl.

The action just described may be better understood by referring to theillustrative and generally self-explanatory curves of Fig. 2 whereincurves 8| and 82 represent, respectively. the gridcathode voltage oftubes 35 and 36, the horizontal line 83 representing the cut-offgrid-cathode voltage of tubes 35 and 38, and the curve 84 represents theregulator characteristic.

There will be a certain range of load currents during which both tubes35 and 38 will conduct. This produces the knee of the regulatorcharacteristic as shown between the dotted lines m and n in Fig. 2 andprovides for stable switching. Due to the gain of the two triodes, theirrelative impedances are kept high so that cut-over from voltage tocurrent regulation or vice versa will be sharp. During the cut-overperiod both the current and the voltage amplifiers exercise control overcurrent flowing through the cathode resistor 43 in varying amounts andhence jointlv control the rectifier input. In addition to their actionas an electronic switch, the tubes 35 and 36 each amplify the signalsimpressed on their grids by their respective control amplifiers with theresistor 43 furnishing negative feedback.

In review, current supplied to the saturating winding IQ of the reactorI8 is controlled by th final amplifier 34 in response to load voltagevariations unless the load current should increase sufiiciently to causethe electronic switch 35-35 to disconnect the voltage amplifier 3! fromthe final amplifier 34 and connect the current amplifier 32-33 thereto.The saturating current would then be controlled in response to loadcurrent variations.

In the event of a failure within the regulating circuit, there isprovided overload protection comprising the relay 31, condenser 85 andthe resistor 86. The fixed grid bias of the series regulating tube 23,which is supplied from the negative terminal of the unregulated supply39 through the resistor 48, also serves to charge the condenser 85 witha polarity as indicated in the figure. The relay 31 has its windingconnected across the resistor 44 and is adjusted to operate at apredetermined safe maximum load current. When operated, the relaypermits the condenser 85 to discharge through the resistor 86 and itscontact and armature to ground. This discharge causes a rapid anddrastic decrease of the grid potential of tube 23 to a degree thatovercomes any abnormal output of the final amplifier 34, and causes areduction in the rectifier I0 input by reducing the current through thesaturated winding IS. This action will be intermittent as long as theoverload condition persists and will occur at a rate determined by thecharging and discharging time of the condenser 85.

There are also provided as' shown in Fig. 1 two regulated rectifiers 81and 88 similar to the one shown and described in detail. The outputs ofthese three rectifiers are connected in parallel to supply current tothe battery l3 and load [4. As previously mentioned, the regulators ofthe parallel rectifiers are interconnected by relatively high impedanceresistance coupling between the voltage amplifiers of the identicalrectifiers. As illustrated, this coupling comprises the three resistors89 which directly connect the control grids of the voltage amplifiers 3|in the several regulators. Alternatively, or, in addition, the cathodesand anodes thereof may be coupled in a similar manner. Variations withinany one regulator are thus reflected to each of the others by an amountdependent on the size of the resistors 89 so that if the recti fiers areinitially adjusted to properly share the load, they will continue to doso in spite of any such variations. must be low enough to keep theoutput currents in reasonable balance, yet high enough so that a failureof one rectifier or regulator circuit will not feed back too great areflection to the other regulators and thus induce hunting.

Although the invention has been described in detail as relating to aspecific illustrative embodiment, other embodiments will readily occurto one skilled in the part without departing from the spirit and scopeof theinvention.

What is claimed is:

1. A system for supplying direct current to a load comprising arectifier having an input and an output, variable means connected tosaid rectifier for supplying alternating current thereto, regulatingmeans for said rectifier comprising means to derive a first voltagewhich varies in accordance with the voltage of said load, means toderive a second voltage which varies in ac-- cordance with the loadcurrent of said rectifier, means controlled in response to said firstvoltage to control said variable means, and switching means to transfercontrol of said variable means from said first voltage to said secondvoltage comprising a pair of space current paths connected in paralleland a control electrode in each of said paths to vary the space currenttherein.

2. A system for supplying direct current to a load which comprises aplurality of rectifiers and regulators according to claim 1, meansconnecting the outputs of said rectifiers in parallel to supply saidlead, and impedance means coupling the said first voltage derivationmeans of each of said rectifiers, each with the other.

3. The combination according to claim 1 and means to apply said firstvoltage to one of said control electrodes and means to apply said secondvoltage to the other of said control electrodes.

4. The combination according to claim 3 wherein said variable means arecontrolled in response to the net space current of said parallel paths.

5. The combination in a regulated rectifier connected to supply directcurrent from a power source to a load-of a first and a second spacedischarge device, means connected to said first device to control thespace current therein in accordance with the voltage of said load, meansconnected to said second device to control the space current therein inaccordance with the load current of said rectifier, means controlled bythe space current of said first device to regulate the power input ofsaid rectifier, and switching means to transfer control of saidlastnamed means from the space current of said first device to the spacecurrent of said second device at a predetermined load current comprisinga pair of space current paths connected in parallel and a controlelectrode in each of said paths to control the space current therein.

6. A system for supplying direct current to a load which comprises aplurality of regulated rectifiers according to claim 5, means to connectthe outputs of said rectifiers in parallel to supply said lead, andimpedance means which couple the said first space discharge devices ofeach of said regulators, each with the other.

7. The combination according to claim 5 and means to impress on one ofsaid control electrodes a voltage varying in accordance with the spacecurrent of said first device and means to The size of these resistorsimpress on the other of said control electrodes a voltage varying inaccordance with the space current of said second device.

' 8. In combination, means for rectifying alternating current suppliedthereto and for supplying the rectified current to a load, means forsupplying alternating current to said rectifier, and regulator means forsaid rectifier comprising a first space discharge device whose spacecurrent is responsive to variations in the voltage of said load, asecond space discharge device whose space current is responsive to theoutput current of said rectifier, variable means controlled by saidvoltage responsive space discharge device for regulating the input tosaid rectifier, and switching means adapted to transfer control of saidinput regulating means from said voltage responsive device to saidcurrent responsive device if the said output current should increase.beyond a, predetermined value comprising a space current path having twocontrol electrodes, an anode, and a cathode, means to control thevoltage on one of said control electrodes with respect to said cathodeby the space current of said voltage responsive device and means tocontrol the voltage of the other of said control electrodes with respectto said cathode by the space current of said current responsive device.

9. The combination according to claim 8 wherein said variable means arecontrolled by the current flowing in said space current path.

10. A system for supplying direct current to a load which comprises aplurality of said first mentioned means each connected to a said loadand regulator means for each of said first mentioned means according toclaim 8, and.im-- pedance means connecting the said first spacedischarge devices of each of said regulator means each with the other.

11. The combination in a regulated rectifier whose output is connectedto supply a load of a first space discharge device whose space currentis caused to vary in accordance with the voltage of said load, a secondspace discharge ll device whose space current is caused to vary in ofthe space current of said first space discharge 80 device, and means totransfer control of said variable means from the space current of saidfirst space discharge device to said second space discharge devicecomprisinga pair of space discharge devices, each having an anode, acathode, and a control electrode, connected in parallel between saidfirst and second space discharge devices and said variable means.

12. A system for supplying direct current to a load comprising aplurality of regulated rectifiers according to claim 11, meansconnecting the outputs of said rectifiers in parallel to supply saidload, and means comprising an impedance to couple the said first spacedischarge devices of v the said plurality of regulators. each with theother.

13. The combination according to claim 11 and means to impress on one ofsaid control electrodes with respect to its associated cathode a'voltagevarying in accordance with the space current of said first spacedischarge device and means to impress on the other of said controldischarge devices, and said variable means connected to said resistanceto derive a control voltage therefrom.

1 5. In combination, means for rectifying alternatmg current suppliedthereto, and for supplying the rectified current to a load, variablemeans for supplying alternatingcurrent to said rectifier, regulatingmeans for said rectifier comprising a first space discharge device,means to cause the space current of said first device to vary inaccordance with the voltage of said load, a second space dischargedevice, means to vary the space current of said second device inaccordance with the rectified current of said rectiflena third and afourth space discharge device each having an anode, a cathode and acontrol electrode, means connecting said anodes to each other and meansconnectingv said cathodes to each other, means to derive a voltage whichvaries in accordance with the space current of said first device and toimpress said voltage on the control electrode of said third spacedischarge device with respect to its cathode, means to derive a voltagewhich varies in accordance with the space current of said second spacedischarge device and to impress said voltage on the control electrode ofsaid fourth device with respect to its cathode, a resistance in serieswith the parallel combination of said third and fourth space dischargedevices, and means connecting said variable means to said resistance toderive a control voltage therefrom.

16. A system for supplying direct current to a load comprising aplurality of regulated rectifiers according to claim 15, meansconnecting the outputs of said rectifiers in parallel to supply saidload, and means comprising an impedance to couple the said first spacedischarge devices of the said plurality of regulators, each with theother.

1'7. A system for supplying direct current to a load comprising aplurality of rectifiers each having an input and an output, meansconnecting said outputs in parallel for supplying said lead, variablemeans for supplying alternating current to each of said inputs, voltageresponsive means for each of said rectifiers which derive a voltagevarying in accordance with the voltage of said load, means comprisingthe said derived voltage to control the said variable means, andimpedance means inter-connecting the said voltage responsive means eachwith the other.

18. In combination, means for rectifying a1- temating current suppliedthereto and for plying the rectified current to a load, means forsupplying alternating current to said rectifier, a saturable reactorconnected in said alternatin current supply circuit, said saturablereactor he ing a saturating winding, a space current de having at leasta plate, a cathode and a pair on one of said control electrodes withrespect electrodes with respect to its associated cathode avoltage'varying in accordance with the space current of second spacedischarge device.

to said cathode,-means to impress said second voltage on the other ofsaid control electrodes. with respect to said cathode, a source ofdirect current, and means under control of the space current in'saidspace current device for supplying current from said direct-currentsource to saiai saturating winding.

ternating current supplied thereto and for supplying the rectifiedcurrent to a load, a source of alternating current, variable means forsupplying current from said source to said rectifier, a first spacecurrent path comprising a plate, a cathode and a control electrode, asecond similar space current path connected in parallel therewith, meansto derive a first voltage proportional to the output voltage of saidrectifier, means to derive a second voltage proportional to the saidrectified current, means comprising said first voltage for controllingthe current in said first space current path, means comprising saidsecond voltage for controlling the current in said second space currentpath, and said variable means controlled by the net space current ofsaid parallel paths.

20. In a system for supplying rectified current to a load comprising asource of alternating current, rectifying means and variable means forsupplying current from said source to said rectifier, a pair of spacecurrent devices connected in parallel, control electrodes in each ofsaid devices for controlling the space current therein, means to impresson one of said electrodes a voltage varying in accordance with theoutput voltage of said rectifier, means to impress on the other of saidelectrodes a voltage varying in accordance with the output current ofsaid rectifier, and means to control said variable means by the netspace current of said space current devices.

JAMES A. POTTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,128,771 Forssell et al Aug. 30,1938 20 2,331,131 Moyer Oct. 5, 1943 2,331,411 Milarta Oct. 12, 19432,413,941 Bixby Jan. 7, 1947

